The injury will definitely rule Guti out of the game with Osasuna, but also makes him a doubt for the 'clásico' against Barcelona in midweek, although Madrid could already have the league title sewn up before they even take to the field against their great rivals.
Guti suffered a twisted left-knee and was unable to take part in any of Wednesday's training session as he spent the time inside Madrid's facilities undergoing physiotherapy work on the injury.
"He has suffered a contusion and twist of the external lateral ligament of the left-knee," the club's medical statement read.
Christoph Metzelder was the only other player missing from the session, also through injury, while Ruud van Nistelrooy continued his recovery from injury by taking part in a small-sided game with the rest of the squad in an attempt to prove his fitness to coach Bernd Schuster ahead of the weekend game.
The Dutch striker has all but shrugged off the right ankle problems that forced him to have surgery to alleviate the issue and is fully expected to be among the squad of eighteen players that Schuster picks to square off against relegation threatened Osasuna on Sunday.
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